Research On Large Signal Modeling For Millimeter-Wave CMOS Transistor

The market demand of smart home,mobile phone and other wireless communication equipment makes RF integrated circuits step into the process of rapid development.Due to its mature technology,low cost and high integration,CMOS technology has been widely used in RF front-end integrated circuits in communication systems.In circuit design,simulation plays an important role in improving the performance and success rate of integrated circuits.The accuracy of the Spice transistor model directly affects the accuracy of the circuit simulation.Therefore,accurate device models are the fundamental to circuit design.As the CMOS process continues to scale down,the cutoff frequency of the transistor continues to increase.In addition,the device exhibits electromagnetic effects and harmonic effect are more complicated at higher frequencies.How to obtain accurate high-frequency device models has become the key to research.In this paper,a series of research work around the nonlinear large-signal model of the transistor are carried out,aiming to improve the accuracy of the transistor model.Firstly,based on the research of previous transistor de-embedding methods,an improved open-short de-embedding equivalent circuit model is proposed in this paper.The model considers the loss of metal vias and the capacitive coupling effect between different layers of metal between the terminals in the open de-embedded structure.The terminal coupling effect in the short de-embedded structure is considered.After measuring the de-embedding structures,the model calculated results were compared with the measurement data.The comparison results show that the accuracy of the new openshort model was improved.The RMSE of scattering parameter is within 0.0145 for open,while RMSE of short model is within 0.0082.Secondly,considering the non-negligibility of the channel current magnetic field effect when the size of the transistor is large,an improved small signal equivalent circuit model is proposed.In this model,a series RL branch is used to characterize the channel current magnetic field effect.Compared with the classical small signal model,this model significantly improves the accuracy in the 0-2GHz frequency band.The root-mean-square error of the S parameter is within 0.063.Based on the small signal model,the nonlinear large-signal model is studied and improved in this paper.Firstly,the nonlinear capacitance model is established and modified.The large signal model of the transistor is completed based on the small signal model,current model and capacitance model.To verify the large-signal model,transistor was manufactured and measured.Compared with the measurement data,this large signal model achieves high accuracy in terms of output power,gain,and additional power efficiency.The root-mean-square-error(RMSE)are less than 0.233 dBm for output power,0.65% for power additional efficiency,and 0.23 dB for the gain respectively.